Ding Du

N-Heterocyclic Carbene-Catalyzed Three-Component Domino Reaction of Alkynyl Aldehydes with Oxindoles

A new and stereoselective synthetic approach to spirooxindole 4H-pran-2-one derivatives with three contiguous stereogenic centers has been developed via an NHC-catalyzed three-component domino reaction of alkynyl aldehydes with oxindoles. The reaction proceeds smoothly in good yields with good to high diastereoselectivities. These novel heterocyclic spirooxindoles may provide promising candidates for drug discovery. Additionally, a possible mechanism for the entire reaction sequence is proposed.

N-Heterocyclic Carbene-Catalyzed Formal [3 + 2] Annulation of α-Bromoenals with 3-Aminooxindoles: A Stereoselective Synthesis of Spirooxindole γ-Butyrolactams

A stereoselective synthetic approach to spirooxindole γ-butyrolactams is developed via N-heterocyclic carbene-catalyzed formal [3 + 2] annulation of α-bromoenals with 3-aminooxindoles. An enantioselective variant of this methodology is also investigated resulting in good substrate tolerance and high enantioselectivities.

Formal [3 + 3] annulation of isatin-derived 2-bromoenals with 1,3-dicarbonyl compounds enabled by Lewis acid/N-heterocyclic carbene cooperative catalysis

A series of novel isatin-derived 2-bromoenals were synthesized and applied in a formal [3 + 3] annulation with 1,3-dicarbonyl compounds enabled by a NHC/Lewis acid cooperative catalysis strategy. This newly developed methodology offers rapid access to functionalized spirooxindole δ-lactones. The newly synthesized isatin-derived 2-bromoenals may be further used as potential electrophilic 1,3-synthons for the diversity-oriented synthesis of spirooxindoles.

Formal [3 + 4] Annulation of α,β-Unsaturated Acyl Azoliums: Access to Enantioenriched N–H-Free 1,5-Benzothiazepines

An unprecedented formal [3 + 4] annulation of α,β-unsaturated acyl azoliums with 2-aminobenzenethiols has been utilized to synthesize enantioenriched N-H-free 1,5-benzothiazepines, which are recognized as privileged structures in numerous biologically active scaffolds. This protocol offers a rapid and direct pathway to access the target compounds with high enantioselectivities and has been applied in the concise synthesis of chiral drug (R)-thiazesim.

Alkynyl Acylammoniums as Electrophilic 3C Synthons in a Formal [3 + 3] Annulation: Access to Functionalized 4H-Pyran-4-ones

Alkynyl acylammoniums generated in situ from alkynyl acids are first used as electrophilic 3C synthons in a formal [3 + 3] annulation with 1,3-dicarbonyl compounds for regioselective synthesis of functionalized 4H-pyran-4-ones via a 4-(dimethylamino)pyridine/Lewis acid dual-activation strategy. This protocol paves the way for further investigation of alkynyl acylammoniums as 3C synthons for construction of diverse heterocyclic skeletons.

Organocatalytic C–C bond activation of cyclopropenones for ring-opening formal [3 + 2] cycloaddition with isatins

Cyclopropenones were first applied as potential 3C synthons in ring-opening formal cycloaddition via an organocatalytic C–C bond activation strategy. This [3 + 2] cycloaddition of cyclopropenones with isatins catalyzed by using two different Lewis bases offers rapid access to spirooxindoles 3 and 4 regioselectively. These findings will provide helpful guidelines for further investigation of the reactivity of cyclopropenones with organocatalysis.

Esters as Alkynyl Acyl Ammonium and Azolium Precursors: A Formal [2 + 3] Annulation with Amidomalonates via Lewis Base/Lewis Acid Cooperative Catalysis

Esters are for the first time used as α,β-unsaturated alkynyl acyl ammonium and azolium precursors to undergo a formal [2 + 3] annulation with amidomalonates through DMAP/LiCl or carbene/LiCl cooperative catalysis. A wide range of (Z)-5-amino-3-furanones were obtained in moderate to high yields with high regioselectivity and stereoselectivity. In addition, a plausible mechanism based on the calculated charge distribution of the intermediates is proposed to explain the regioselectivity.

Frontispiece: Direct and Enantioselective Synthesis of N−H-Free 1,5-Benzodiazepin-2-ones by an N-Heterocyclic Carbene Catalyzed [3+4] Annulation Reaction

An NHC-catalyzed formal [3+4] annulation of α,β-unsaturated acylazoliums with protecting-group-free aryl 1,2-diamines was developed for a direct and highly enantioselective synthesis of 4-aryl N-H-free 1,5-benzodiazepin-2-ones. This methodology offers an efficient and rapid access to a wide range of enantioenriched target compounds from easily accessible starting materials. The protocol is also scalable and the desired products can easily undergo subsequent N-functionalization to afford diverse N-substituted derivatives. Additionally, a mechanism was proposed to explain the high enantioselectivity in this process.

N-Heterocyclic Carbene-Catalyzed Formal Conjugate Hydroacylation: An Atom-Economic Synthesis of 1H-Indol-3-yl Esters

An atom-economic synthesis of useful 1 H-indol-3-yl esters has been demonstrated by an N-heterocyclic carbene (NHC)-catalyzed formal conjugate hydroacylation of 2-phenyl-indol-3-ones with readily accessible aldehydes. This reaction involves a reductive hydride transfer process that was rarely investigated in the field of NHC catalysis. In this process, the hydrogen from the aldehydes was formally transferred to a heteroatom with NHC catalysis for the first time.